1. Field of the Invention
The present invention relates generally to arrangements for preventing the ingress of precipitation to expulsion-type circuit interrupters and more particularly to an improved rain shield for such circuit interrupters.
2. Description of the Related Art
High-voltage circuit interrupters and particularly high-voltage expulsion-type fuses are well known in the art. For example, U.S. Pat. Nos. 3,267,235, 3,575,683, 3,176,100, 3,855,563, 4,153,893, 4,158,830 and 4,193,053 illustrate typical fuses for high-voltage electric power circuits and particularly those of the expulsion type. Such high-voltage circuit interrupters are often mounted outside on utility poles and thus are directly exposed to adverse weather conditions including rain, sleet, hail, and snow. In addition, it is common for circuit interrupters of this type to have an inverted, drop-out position (also referred to as a drop-down position). For some circuit interrupters, this position results via normal operation after circuit interruption. Additionally, the circuit interrupter may be manually opened to the inverted position by the use of appropriate handling tools. Since such high-voltage fuses usually comprise an arc-quenching or arc-extinguishing material such as boric acid, etc., which if exposed to excessive moisture will be degraded, various arrangements are utilized to reduce deleterious effects that may result from moisture ingress.
In order to provide protection against the direct ingress of precipitation and especially when the circuit interrupter is in the inverted, drop-out position, rain shields may be provided. Rain shields of both the gravity-operated flapper type and the clamp-on type are illustrated in Descriptive Bulletin 242-30 dated Apr. 30, 1984 at pages 12-15 for S&C Power Fuses-Types SM-4 and SM-5 manufactured by S&C Electric Company. While such rain-shield arrangements are very useful to help prevent the ingress of precipitation, such designs cannot be fully effective under all conditions, for example, with high winds and driving rains.
Various sealing methods can be utilized to prevent the ingress of moisture to the interior of the circuit interrupter. However, such methods may, over time, develop leaks.
U.S. Pat. No. 4,045,758 discloses an arrangement which aids in preventing lower than atmospheric pressures from being developed on the inside of the circuit interrupter due to temperature cycling and permits the interchange of air between the interior and the environment. A breather assembly, as disclosed in U.S. Pat. No. 4,047,142 permits atmospheric venting to the interior while preventing precipitation from entering the circuit interrupter. While the breather assembly is useful, the breather assembly is not reusable and is not practical for use with circuit interrupters having higher interrupting ratings.